1. Field of the Invention
The present invention relates to a photoelectric conversion device used in a digital camera or the like, which forms an image by converting incident light to an electric charge.
2. Related Background Art
For an image input device like a digital camera, a video camera and an image reader, a photoelectric conversion device is used such as a CCD (Charge Coupled Device) image sensor, or a non-CCD image sensor like a bipolar transistor image sensor, a field-effect transistor image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor and the like. The photoelectric conversion device converts optical image information to an electric signal, and the image input device processes these various converted electric signals to display them on a display for indication or record them in a storage medium.
In order to acquire high performance, a photoelectric conversion device is desired to increase the number of photoelectric conversion elements to be arranged thereon, by reducing the area (picture element area) of a photoreceiving region of the photoelectric conversion element, and to reduce its chip size. Such a photoelectric conversion device has a microlens arranged on a photo diode. The structure is designed so that the focal position is set in the vicinity of a photoreceiving portion of the photo diode.
However, as picture elements are compacted and a tip is downsized, a smaller proportion of a light condensed by a microlens enters a photoreceiving portion. As a result, a photoelectric conversion device causes the lowering of its sensitivity. Particularly when the photoelectric conversion device has taken a low F number (the aperture is fully opened), or when a camera or the like has been designed to have a short focal length between a lens and the photoreceiving portion, the problem becomes remarkable in a peripheral region of in a pixel region.
In recent years, as a method for solving such a problem, Japanese Patent Application Laid-Open No. 2000-150845 proposes a photoelectric conversion device having a optical wave-guide. FIG. 4 is a typical sectional view showing one configuration example of a conventional photoelectric conversion device. The conventional configuration will be now briefly described with reference to FIG. 4.
In the configuration shown in FIG. 4, an interlayer insulation layer 7 having a well structure 21 is formed right above a photoreceiving portion 2. The well structure 21 has a large refractive index layer 8 consisting of a material having a large refractive index than the interlayer insulation layer 7, and reflects incident light 15 which has passed through the on-chip-microlens 11, on an interface between the large refractive index layer 8 and the interlayer insulation film 7. Thus, a conventional photoelectric conversion device increases condensing efficiency and enhances sensitivity. Here, the conventional photoelectric conversion device has an etching-stop layer 12 thereon, in order not to damage the photoreceiving portion 2 and improve the uniformity of an etching depth when the well structure 21 is formed.
However, the etching-stop layer 12 occasionally causes the reflection of the light coming from the upper part on the interface between a large refractive index layer 8 and itself, due to a difference of the refractive index between them. The reflection on the interface causes reduction and variation in sensitivity. In addition, Japanese Patent Application Laid-Open No. 2000-150845 proposes a photoelectric conversion device having a patterned etching-stop layer 12 arranged on one part of a photoreceiving portion. In such a configuration, a region of the photoreceiving portion having the etching-stop layer 12 provided thereon shows reflectance different from that on the region having no film thereon, because the regions have different refractive indices; and particularly, the edge part of the etching-stop layer 12 reflects incident light thereon to decrease condensing efficiency.
In order to solve the above described problem, the present invention is directed at providing a photoelectric conversion device which inhibits sensitivity from lowering and varying, and providing a production method therefor.